This invention relates to .beta.-lactam antibiotics. In particular, it relates to a process for preparing certain 4-substituted azetidinones, primarily useful as intermediates to .beta.-lactam antibiotics.
Among the newer .beta.-lactam antibiotics currently under investigation are the 1-carba(1-dethia)-3-cephem-4-carboxylic acids. These .beta.-lactam compounds provide significant synthetic challenges. One of the more noteworthy approaches to total synthesis of 1-carba(l-dethia)-3-cephem-4-carboxylic acids is the asymmetric route described by Evans, et al., U.S. Pat. No. 4,665,171.
One further route to cis-chiral azetidinones with readily derivatized 4-allyl (and substituted allyl) groups, is provided by Blaszczak, U.S. Pat. No. 4,771,134. The Blaszczak method utilizes a 4-acetoxy azetidinone as starting material to provide 4-(substituted selenyl)azetidinones. The 4-(substituted selenyl)azetidinones are converted to 4-allyl(and substituted allyl)azetidinones under free radical conditions using a (2-substituted or unsubstituted) allyl tin reagent.